There are known centrifugal liquid pumps which have a housing section defining a rotational axis of the pump, with an intake cavity defining an annular area generally perpendicular to the rotational axis. An intake port leads to the cavity generally radially of the axis. An impeller section is located in communication coaxially with the intake cavity of the housing section for pumping the liquid out of the cavity. The impeller section conventionally includes a rotatable impeller.
Such pumps often are used in environments wherein the pumped liquid contains contaminants, such as contaminant particles. One such environment is in the application of fuel pumps where the fuel may contain contaminating particles. These pumps normally operate at high speeds and the impeller provides a suction head that draws the fuel carrying the contaminant particles through the inlet port, around the intake cavity and into the impeller section of the pump.
However, problems occur with the contaminant particles when the pump is idling at a low R.P.M. or at low flow conditions. In this state of operation, there is an insufficient suction head to draw the fuel with its entrained contaminants from the intake cavity into the impeller section. This state of operation can have extended duration in such applications as aircraft fuel pumps. The problem is that the contaminant particles build up in a wall of sludge about the outer bounds of the intake cavity. Therefore, upon an increase of speed of the pump, this concentrated mass of contaminants will immediately pass into the fuel system rather than be evenly dispersed in the fuel as may be expected. Furthermore, a major problem is caused by the continuous circular movement of the concentrated contaminant particles about the inlet cavity as the particles impinge upon the cavity walls. This causes considerable wear and may even deteriorate the walls to an extent which would cause pump inlet leakage.
Some prior art solutions to the above problems, particularly the potential wear-through problem, involve armor plating the walls of the inlet cavity to withstand the erosion thereof created by the continuous movement of the contaminant particles. Such solutions not only are expensive but face the additional problem of providing fuel-compatible armor materials.
This invention is directed to solving the above problems by a novel configuration of the intake cavity such that the contaminant particles are moved into the fuel system regardless of the speed or the flow rate of the fluid.